Refrigeration systems used in apparatuses for cooling objects to be cooled such as a refrigerator, a freezer, a cooling apparatus, etc. are constructed by substantially the same constituent elements on the basis of the same principle irrespective of the scale or application of the system.
FIG. 4 is a diagram showing the construction of a general refrigeration system. As shown in FIG. 4, a general refrigeration system comprises a compressor 1, a condenser 13, a receiver tank 14, an expansion valve 15 and an evaporator 11 which are connected to one another through a refrigerant pipe 22, and refrigerant filled in this system transfers heat while circulated in a direction of an arrow 21 in the system. This circulation of the refrigerant is called as a refrigeration cycle. There is a case where a capillary tube is used in place of the expansion valve 15. In this case, the capillary tube is a very narrow tube of about 0.8 mm in inner diameter, for example.
Refrigerant gas is compressed in the compressor 1, and fed as high-temperature and high-pressure refrigerant to the condenser 13. In the condenser 13, the high-temperature and high-pressure refrigerant gas radiates heat, so that the refrigerant concerned is cooled to obtain intermediate-temperature refrigerant liquid. This intermediate-temperature refrigerant liquid is temporarily stocked in a receiver tank 14.
When the expansion valve 15 is opened, the intermediate refrigerant liquid enters the evaporator 11 which is reduced in pressure because the refrigerant gas thereof is sucked by the compressor 1. The intermediate refrigerant liquid is evaporated in the evaporator 11 and the temperature thereof is reduced by evaporation heat, so that the intermediate refrigerant liquid becomes low-temperature refrigerant liquid. The low-temperature refrigerant liquid absorbs heat from the surrounding thereof and thus cools the surrounding (targets to be cooled), and at the same time, it becomes low-temperature refrigerant gas. The low-temperature refrigerant gas is fed into the compressor 1, compressed again to become high-temperature and high-pressure refrigerant gas, and then circulated as high-temperature and high-pressure refrigerant gas.
As described above, the refrigerant is circulated in the refrigeration cycle while the heat obtained by cooling the surrounding targets in the evaporator 11 is radiated in the condenser 13 by the refrigerant.
In the evaporator 11, as shown in a phase change diagram of refrigerant shown at the lower side of the evaporator 11 of FIG. 4, most of the refrigerant is liquid in the neighborhood of the inlet of the evaporator 11, however, the refrigerant is gasified and the amount of the gasified refrigerant increases as it goes through the evaporator 11, so that the refrigerant is perfectly gasified in the neighborhood of the outlet of the evaporator 11. It is said that it is best in efficiency to perfectly gasify the refrigerant in the evaporator. However, in general, the refrigerant is perfectly gasified before the outlet of the evaporator 11 and the temperature further increases.
FIG. 5 is a diagram showing the construction of a refrigeration cycle which is generally used for a domestic refrigerator or the like at present. Refrigerant (chlorofluorocarbon (CFC), CFCs substitute or the like) which is sealingly filled in the refrigeration cycle is circulated in a direction of an arrow 21. First, refrigerant is compressed into high-temperature and high-pressure refrigerant gas by the compressor 1, and air-cooled in the large-size condenser 13 to be condensed and liquefied (roughly, a state of 90% liquid and 10% gas is kept). Then, the refrigerant is passed through the receiver tank (liquefying tank) 14, and expanded and reduced in pressure in the expansion valve 15 to become low-temperature and low-pressure refrigerant liquid. Thereafter, the low-temperature and low-pressure refrigerant liquid is fed to the evaporator 11 and heat-exchanged in the evaporator 11 (freezing temperature in a refrigerator or the like), whereby the refrigerant is evaporated and gasified to become low-temperature refrigerant gas, and returns to the compressor 1. The condenser 13 is provided with a cooling fan 13-1 to be enforcedly cooled as occasion demands in a special apparatus such as an industrial refrigerator or the like. In the condenser 13, the pipe through which the refrigerant flows and the air surrounding the pipe are brought into contact with each other to be heat-exchanged with each other, thereby cooling and liquefying the refrigerant. Therefore, it is preferable that the surface area of the pipe is broad and the occupational area of the evaporator 13 in the overall refrigeration system is increased.
In such a refrigeration system, the condenser 13 serving as a heat-source side heat exchanger must be designed to have a larger structure as compared with the evaporator 11 serving as a heat exchanger, and thus various studies have been made to miniaturize the condenser 13 so that the apparatus is designed to be compact. For example, Patent Document 1 discloses a refrigeration system in which a part of high-temperature and high-pressure refrigerant gas discharged from a compressor is cooled through a spiral tube by a cooling fan while the remaining high-temperature and high-pressure refrigerant gas discharged from the compressor is efficiently cooled by the former cooled refrigerant gas. Furthermore, Patent Document 2 discloses a system in which refrigerant discharged from a compressor is cooled through a spiral tube by a cooling fan, and further reduced in pressure and liquefied by another narrow tube.    Patent Document 1: JP-A-10-259958    Patent Document 2: JP-A-2002-122365